The invention relates to a multipole low voltage circuit breaker high currents, housed in a molded insulating case, each pole comprising:
a plurality of movable contact fingers of the same length extending parallel to the fingers slightly apart from one another, and being driven in unison between a closed position and an open position by a mechanism.
a stationary main contact cooperating in the closed position with a movable main contact of each contact finger,
a pair of connection pads in electrical connection with the stationary main contact and the contact fingers,
an arc extinguishing chamber having a stack of deionizing metal plates with a pair of conducting horns for guiding the migration of the arc, one of the stationary horns being in electrical connection with the stationary main contact and having an intermediate edge extending past the stationary main contact along the direction of movement of the front extensions of the contact fingers, thereby limiting lengthening of the arc during the initial separation phase.
A state-of-the-art circuit breaker of the kind mentioned is described in U.S. Pat. No. 4,764,650, and enables very intensity short-circuit currents to be interrupted. The arc is prevented from returning to the arc formation zone by the presence of the edge on the stationary arc guiding horn. The separable contacts act as both main contacts and arcing contacts. Tests have revealed that the arc may stagnate, causing premature erosion of the contacts depending on the type of fault, notably in the presence of direct currents.
In the circuit breaker described in U.S. Pat. No. 4,295,022, the center contact finger alone supports the movable arcing contact, and is of greater length than the juxtaposed contact fingers supporting the movable main contacts. The arcing contacts are always closed in the closed position of the circuit breaker. Fitting two types of contact fingers complicates the manufacture of each circuit breaker pole.
The object of the present invention is to improve the electrical withstand of a low voltage circuit breaker for high currents.